Having just read the NTSB extract, I note that the initial posting from SASless omits a significant point: the aircraft was equiped with a Honeywell SPZ-7600 autopilot. This would mean it was capable of being full coupled in all 4 axis, and equiped with a rad-alt, although obviously it wasn't equiped with an alerting device.
The recommendations include reference to training in the use of the autopilot, especially the coupling cues and annunciations. One can only wonder what modes were engaged at the time of the accident: none, IAS only, V/S? Not ALT I guess!
I forget the logic of the undercarriage audio warning, but would this not have triggered as the a/c descended through the rad-alt bug setting? Unless the rad-alt bug was set to zero (annoying bright orange lights at night?)